Effect of Mn doping on the densification and properties of transparent alumina by high-pressure spark plasma sintering

It is common practice to control the densification and microstructure of alumina using additives or dopants. In the present study, the effect of Mn-doping on the sintering behavior, optical properties, microstructure, and mechanical properties of alumina was examined. Addition of 0.5 at.% Mn was shown to significantly reduce densification rate and grain growth during high-pressure spark plasma sintering (HPSPS). The major effects resulted from the formation of MnAl2O4 nano inclusions located at grain boundary triple points. The Mn-doped alumina was highly transparent and had a light-brown tint due to absorption between ∼410 and 580 nm and a cutoff at 300 nm. The MnAl2O4 nano-inclusions caused the Young's modulus to decrease from 400 ± 5 GPa for pure alumina to 370 ± 5 GPa for Mn-doped alumina, while the fracture toughness increased from 2.97 to 3.66 MPa m0.5, and the hardness was the same. Thus, the addition of Mn enables control of the transparent alumina densification process and microstructure development, and it can be used to tailor the optical and mechanical properties for specific applications.